The efficiency of a communication system is basically determined by the bandwidth used and the signal to noise ratio in the receiver according to the expression formulated by Claud Elwood Shannon in 1948:
                    C        =                  B          ⁢                                          ⁢                                    log              2                        ⁡                          (                              1                +                                                      P                    s                                                        N                    s                                                              )                                ⁢                      (                          bits              ⁢                              /                            ⁢              sec                        )                                              (        1        )            
Increasing the bandwidth entails using a resource which is becoming more and more scarce due to the considerable number of telecommunication services that society demands. The only factor we can alter is the signal to noise in reception,
            P      s              N      s        .
It is not desirable to increase the transmission power, Ps, since the consumption of the equipment must be as reduced as possible, especially in mobile equipment. Therefore, the only element susceptible to being reduced is the noise power in the receiver. Most noise reduction techniques make use of the statistical properties of the noise to be considered.
Generally, although not always, the noise with which communications systems are modeled is the Gaussian white noise, the spectral power density of which is constant along the entire spectrum of interest. Gaussian white noise is generally associated to the noise temperature or noise factor of the electronic devices used in reception. Generally, the noise is modeled as the noise produced by an equivalent noise resistance (R), in a bandwidth (B) and at the working temperature (T) in Kelvin degrees. In other words:N0=kTBR watts   (2)
where K is the Boltzman constant.
The term noise density in watts per hertz for a 1 ohm resistance is generally used.
One of the most effective techniques for improving the Signal to Noise Ratio (SNR) of a communication system is called the matched filter.
Said technique allows optimizing the SNR assuming that the noise is Gaussian noise. The most significant case is the use of digital encoding systems of the symbols transmitted by means of sequences whose autocorrelation function is as similar as possible to a Krönecker delta. The use of Barker, Willard, Gold, Kasami and Walsh sequences, and many others, has become widespread for this purpose in the majority of the current applications. Thus, the length of the sequences used N allows increasing the signal to noise ratio or reducing the signal level to correctly detect the signal received. This improvement factor is called Process Gain Gp, and can be expressed by:GP=10 log10(N)dB.  (3)
The drawback of this technique is that since each symbol is encoded by a sequence of length N, the bits of which are transmitted at N times the symbol speed, the symbol speed is reduced as the length of the sequences used increases. If it is necessary to maintain the transmission speed, the bandwidth transmitted must be increased, due to which the spectral efficiency of the system decreases with N. In the event that the noise is not Gaussian noise, matched filtering is not the best solution. The techniques for reducing different types of noise will depend on the application and on the features of the communication system.
Based on the foregoing, it can be deduced that there is a necessity for a technique which allows reducing noise without reducing the transmission speed nor increasing the bandwidth used, allowing maintaining, at the same time, the transmitted power and independently from the modulation system used.
Likewise, in numerous applications, a certain degree of privacy is necessary, the complementary sequences are extremely complex to decipher by analytical methods due to their non-reducible sequence quality, due to which at the same time that the signal to noise ratio is improved, it is possible to encipher the information before transmitting it or storing it, and to decipher it in the later reception or reading.
The existence of any patent or utility model having features which are the object of the present invention is not known.